The present invention relates to receivers such as multi-carrier receivers.
An orthogonal frequency division multiplex (OFDM) receiver in a terrestrial digital video broadcast (DVB-T) network is required to operate in a complex channel environment, wherein high power analogue television signals may co-exist. The mix of high power analogue television signals and lower power digital signals results primarily from the concurrent existence of both analogue and digital television services.
FIG. 1 shows an example of a typical section of the UHF spectrum, showing a number of adjacent channels Nxe2x88x921, N and N+1, with each channel occupying 8 MHz bandwidth. The existing analogue channels are distributed in the UHF spectrum according to known frequency planning criteria. Due to the nature of analogue receiver technology, especially when analogue television was first introduced, and the difficulty of achieving adequate channel interference rejection, each analogue channel is separated from the others by a minimum gap of 8 MHz. It is in these gaps that digital channels are broadcast.
FIG. 2 is a block diagram showing a digital video broadcasting (DVB-T) set-top-box receiver 200 according to the prior art. A DVB-T signal is received by an antenna 202. The received signal is amplified by a radio frequency (RF) amplifier 204. The amplified signal is subsequently mixed in a mixer 206 with a signal generated by a local oscillator 214. The mixer 206 reduces the frequency of the received RF signal to that of an intermediate frequency (IF) signal. The IF signal is amplified by an IF amplifier 208, before passing to a demodulator 209 and a forward error corrector (FEC) 210, where demodulation of the signal and error correction takes place. The output 212 from the FEC 210 is a DVB-T transport stream.
Normal network planning assumes that the adjacent analogue channels can be up to 35 dB higher than a digital channel. In order to cope with such high power adjacent channels, and to be able to successfully receive a desired digital channel, the radio frequency (RF) stages of a digital receiver must be highly linear. If a digital receiver is not highly linear, intermediate modulation (IM) products may interfere with the desired signal and prevent good reception. However, current RF amplifiers are not completely linear devices, and exhibit non-linear properties. High linearity can be achieved, however, by having high bias currents in the RF amplifiers of a digital receiver.
According to a first aspect of the present invention, there is provided a receiver for receiving signals conveying information, wherein the receiver includes a non-linear element, the receiver comprising: a demodulator for demodulating the received signal to produce demodulated information; means for determining the quality of the demodulated information; and means for adjusting the linearity of the non-linear element in dependence on the determined quality.
This advantageously allows the power consumption of receivers to be reduced in certain conditions. As people become more environmentally aware, efficient and economic consumer goods becomes increasingly important. Such reductions in power consumption can contribute significantly to power savings for the consumer. The present invention provides further advantages in the field of mobile and portable receivers, wherein reductions in power relates directly to increased operating time from a given battery or portable power unit or can even result in a reduction in size of a battery unit.